Bone Regeneration Material

This application is a Continuation of U.S. patent application Ser. No. 16/477,904 filed on Jul. 15, 2019, which is a National Phase of PCT Patent Application No. PCT/EP2018/050877 having International Filing Date of Jan. 15, 2018, which is a Continuation-in-Part of PCT/EP2017/050779 having International Filing Date of Jan. 16, 2017 and claims the benefit of priority of Belgium Patent Application No. BE2017/5025 filed on Jan. 16, 2017. The contents of the above applications are all incorporated by reference as if fully set forth herein in their entirety

The present invention relates to a bone regeneration material comprising a first solid phase of hydroxyapatite of natural origin which is macroporous having pores of diameters greater than or equal to 50 μm, preferably pores of diameters of between 50 and 100 μm.

Such a bone regeneration material is known from document WO2015/049336 and is used as part of treating bone damage in different fields such as corrective or cosmetic surgery.

Hydroxyapatite is a mineral species from the phosphate family, of formula Ca(PO)(OH). More specifically, hydroxyapatite belongs to the apatite crystallographic family which are isomorphic compounds having one same hexagonal structure. This compound is widely used as a biomaterial for many years in different medical specialities, as hydroxyapatites are the most frequent crystalline calcium phosphates, and the first mineral constituents of bones, tooth enamel and dentine. Moreover, hydroxyapatites (and in particular, hydroxyapatites of natural origin) have good biocompatibility and specific adsorption properties of cells or proteins.

It is thus recognised that hydroxyapatite of natural origin has osteoconductive properties as well as a crystalline structure and a morphology identical to those of a natural bone material in humans, hydroxyapatite consequently perfectly suiting as part of a bone reconstructive or corrective surgery. In this sense, numerous materials comprising hydroxyapatite are currently used as dental implants to stimulate the bone reconstruction on bone sites having defects or damage. In particular, using a natural hydroxyapatite coming from bone samples cleaned of the organic substances thereof (proteins, prions, peptides and lipids) makes it possible to obtain a matrix, particularly specific to bone regeneration compared with the artificial analogue thereof. It is preferable that the bone regeneration material is purified beforehand of any trace of organic substances such that the implant is correctly accepted/integrated by the organism, is biocompatible and can interact by osteoconduction with the biological medium wherein it is placed.

As examples, hydroxyapatites can be used as substitution materials to replace or regenerate diseased or damaged tissues. They are also frequently used as a coating on titanium protheses to facilitate the osteointegration or also can prevent wear due to micromovements between the implant and the bone. Hydroxyapatites can also be used as cement in order to replace autogenic bone grafts. Furthermore, a growing number of hydroxyapatite applications as a medication vector is developed, this because hydroxyapatite has a structure with interconnected micropores.

As mentioned above, hydroxyapatite has a chemical composition very close to that of the mineral phase of the bone and the biological properties thereof as well as the biocompatibility thereof make it an excellent bone substitution product. It is specified that a bone colonisation depends on the porous characteristics of the bone regeneration material and the interconnection between the macropores thereof (number and dimension). These interconnections constitute types of “tunnels” which make it possible for the passage of cells and blood circulation between the pores thus encouraging bone formation.

Hydroxyapatite, through the high biocompatibility level thereof and the slow resorption thereof in the organism, can be administered in different forms and in numerous tissues for various applications. In particular, hydroxyapatite-based malleable cements are distinguished which are prepared then administered on the zone to be treated where they harden. These cements are used as a bone substitute due to the good osteointegration thereof and the bioresorbability thereof making it possible to give way to a neoformed bone over time.

There are also solutions and hydroxyapatite-based gels which can contain a polymer such as carboxymethylcellulose. Thus, bioactive ceramic-polymer composite implants are spoken of, these products can be used in different fields such as to fill periodontal deficiencies in dental surgery or carry out fillings in orthopaedic surgery.

Certain hydroxyapatite-based products are also presented in the form of a block, powder or granules used in orthopaedics, fillings or as a complement to dental implants.

Among hydroxyapatite-based products, numerous are those which are not ready for use and which require a preparation beforehand. It is the case, in particular, for hydroxyapatite-based cements which require a prior mixing of a powder and a solution before deposition on or in a zone to be treated where an in situ hardening is thus carried out. Other hydroxyapatite-based products also require to be shaped before implantation on or in the zone to be treated.

Unfortunately, even if such a bone regeneration material comprising a solid phase of hydroxyapatite of natural origin which is macroporous has properties specific to an endo-osseous implantation and makes it possible for a correct bone regeneration thanks to the biocompatibility thereof and to the osteoconductive capacities thereof, it is observed, in practice, that this type of bone regeneration material is not always optimal and that the timeframe for the bone regeneration process is always relatively long (1 mm/month). Moreover, the bone regeneration quantity is frequently insufficient, which leads to the formation of partial fibroses rather than a total ossification.

With the aim of accelerating the bone regeneration process, document US2002/0114755 discloses a material comprising hydroxyapatite and 50 to 90% by mass of tricalcium phosphate, the material according to this prior document being obtained by converting hard algal tissues in an aqueous phosphate solution with the addition of Mgions at an increased temperature.

The bone regeneration material according to this prior document, i.e. which comprises hydroxyapatite and 50 to 90% by mass of tricalcium phosphate of natural origin, has an interconnected porous structure, an improved and controllable resorption in the organism leading to an accelerated bone regeneration.

Unfortunately, even if a bone regeneration material according to document US2002/0114755 makes it possible to accelerate the bone regeneration process by increasing the calcium and phosphorus contribution in the form of free ions in the direct medium of the implantation site, it is observed that this type of material is not optimal.

Indeed, the method for obtaining such a bone regeneration material consists of transforming hydroxyapatite into tricalcium phosphate. Therefore, this is the conversion of a first natural phase into a second natural phase, hydroxyapatite being replaced with tricalcium phosphate.

Thus, during the implantation of the bone regeneration material according to document US2002/0114755, tricalcium phosphate which is more soluble than hydroxyapatite will quickly be solubilised and release calcium and phosphorous ions in the medium of the implantation site. As mentioned above, the tricalcium phosphate of such a bone regeneration material represents 50 to 90% by mass and is obtained by the conversion of a portion of hydroxyapatite contained in the starting material, namely the hard algal tissue. Consequently, with a bone regeneration material according to this prior document, 50 to 90% of the mass (corresponding to tricalcium phosphate) will quickly be solubilised following the implantation and thus lead to a natural hydroxyapatite material having wide empty zones and therefore to a hydroxyapatite material which is certainly of natural origin but which no longer has optimal topographic characteristics (porosity, specific surface area, etc.) making it possible for a good bone regeneration.

A bone regeneration material according to document US2002/0114755 therefore does not make it possible to maintain, over the long term, the suitable microporous structure of natural hydroxyapatite once this implanted and does not therefore make it possible to ensure an optimal bone regeneration process on the implantation site in terms of proliferation and differentiation of bone cells as such a material, once implanted, no longer has a superficial topography, nor a suitable microporosity.

The invention aims to overcome the disadvantages of the state of the art by providing a bone regeneration material making it possible to minimise the bone regeneration time while stimulating the bone regeneration potential so as to obtain an optimal regenerated bone quantity.

The bone regeneration material according to the invention not only has chemical properties (optimised calcium and phosphorus salting-out in the form of free ions) which make it possible to minimise the bone regeneration time, but also has optimal physical properties (topography and porosity conserved) enabling a good bone colonisation so as to obtain an optimal regenerated bone quantity.

To resolve this problem, a bone regeneration material according to the invention is provided, comprising a first solid phase of hydroxyapatite of natural origin which is macroporous having pores of diameters greater than or equal to 50 μm, preferably pores of diameters of between 50 and 100 μm, said bone regeneration material, the bone regeneration material according to the invention being characterised in that it further comprises a second solid synthetic phase of calcium phosphate intended to enrich said first phase, said second phase having a Ca/P molar ratio of between 0.2 and 2, preferably of between 0.3 and 1.8, preferably between 0.5 and 1.65, said bone regeneration material having a defined weight ratio between said first solid phase of hydroxyapatite of natural origin and said second solid synthetic phase of calcium phosphate of between 99/1 and 1/99.

Advantageously, according to the invention, the defined weight ratio between said first solid phase of hydroxyapatite of natural origin and said second solid synthetic phase of calcium phosphate is 95/5, 90/10, 85/15, 80/20, 75/25, 70/30, 65/35, 60/40, 55/45, 50/50, 45/55, 40/60, 35/65, 30/70, 25/75, 20/80, 15/85, 10/90 or 5/95.

In the scope of the present invention, it has been highlighted that such a bone regeneration material according to the invention having:

Furthermore, it has been observed, surprisingly, that the bone regeneration material according to the invention, i.e. of which the solid phase of hydroxyapatite is a natural phase of hydroxyapatite which is enriched by a second phase of calcium phosphate, has optimal topographic characteristics (porosity, specific surface area, etc.) making it possible to optimise the bone regeneration by enabling a good bone colonisation, and this even after the implantation of the bone regeneration material.

A good bone colonisation depends on the porous characteristics of the bone generation material and the interconnection between the macropores thereof (number and dimensions), these interconnections constituting types of “tunnels”, which make it possible for the passage of cells and blood circulation between the pores encouraging bone formation. The conservation of the topographic characteristics of natural hydroxyapatite is therefore paramount to obtain a suitable bone regeneration, which is not the case with a regeneration material according to document US2002/0114755 where a portion (50 to 90% by mass) of the natural phase of hydroxyapatite is converted into a natural phase of tricalcium phosphate.

A bone regeneration material according to the invention therefore has both optimal chemical and physical properties (optimised calcium and phosphorus salting-out in the form of free ions/topography, porosity) which ensure a bone regeneration and a formation of the bone optimised in a significantly reduced time with respect to a bone regeneration material such as that of documents WO2015/049336 and US2002/0114755.

In particular, in the scope of the present invention, it has been highlighted that, when the defined weight ratio between said first solid phase of hydroxyapatite of natural origin and said second synthetic solid phase of calcium phosphate is of between 99/1 and 1/99, and is preferably 95/5, 90/10, 85/15, 80/20, 75/25, 70/30, 65/35, 60/40, 55/45, 50/50, 45/55, 40/60, 35/65, 30/70, 25/75, 20/80, 15/85, 10/90 or 5/95, the bone regeneration time is significantly reduced. This is due to the fact that with such a ratio, at least one of the calcium and/or phosphorus salting-outs in the form of free ions is such that calcium and/or phosphorus is thus located in the surrounding bone regeneration medium in a quantity making it possible to significantly increase the concentration here with respect to the concentration naturally encountered, while only hydroxyapatite tends to capture calcium and phosphorus in the form of free ions and to deplete the surrounding medium thereof from the bone regeneration site.

It must be noted, that two-phase bone regeneration materials are described in the state of the art, in particular materials consisting of a synthetic hydroxyapatite and synthetic tricalcium calcium phosphate association: these are therefore 100% synthetic materials which, as for a regeneration material such as indicated at the start, impose a relatively long bone regeneration duration. Moreover, such totally synthetic two-phase bone regeneration materials do not make it possible, on the contrary, for a material according to the invention, to ensure an optimal bone regeneration on the implantation site in terms of proliferation and differentiation of bone cells as they do not have a suitable superficial topography nor a suitable microporosity.

Preferably, according to the invention, said second synthetic solid phase of calcium phosphate has a Ks solubility product greater than that of said first phase of hydroxyapatite of natural origin. This is particularly advantageous, since calcium and phosphorus must be contributed in the form of free ions in the direct medium of the implantation site while conserving the structural properties (pore size, specific surface area, etc.) and composition of the solid phase of hydroxyapatite of natural origin. Since the solubility of the second phase is greater, it is mainly this phase in particular which will be at the origin of the calcium and phosphorus release in the form of free ions (for example, Caand PO) and not hydroxyapatite of natural origin, which is clearly less dissolved and which, on the contrary, tends to fix these ions at the start of the implantation medium.

Advantageously, according to the invention, said first solid phase of hydroxyapatite of natural origin has a specific surface area greater than 4 m/g.

Preferably, according to the invention, said second synthetic solid phase of calcium phosphate is selected from the group constituted of monocalcium calcium phosphate (MCP), dicalcium calcium phosphate (DCP), octacalcium phosphate (OCP), calcium deficient apatite (CDA), amorphous calcium phosphate (ACP), tricalcium calcium phosphate (TCP), tetracalcium calcium phosphate (TTCP), and the mixtures thereof.

Advantageously, according to the invention, said first phase of hydroxyapatite of natural origin is hydroxyapatite obtained from a bone material of natural origin, in particular from a bone material of animal origin. For example, hydroxyapatite of natural origin can be hydroxyapatite obtained from a bone material coming from a mammal (bovine, horse, pig or sheep), coral or cuttlefish.

Preferably, according to the invention, said hydroxyapatite of natural origin which is macroporous of said first phase is a hydroxyapatite of natural origin which is macroporous at least partially sintered. The controlled sintering (heating of a powder without leading it to melt) advantageously makes it possible to obtain a hydroxyapatite of natural origin having increased mechanical resistance properties while conserving a suitable microporosity and a suitable surface topography, which makes it possible to facilitate the implantation and to improve the long-term stability after implantation.

Advantageously, the bone regeneration material according to the invention, further comprises at least one therapeutic agent selected in the group constituted of antibiotics, antivirals, anti-inflammatoires, hormones such as steroids, growth factors such as BMPs (Bone Morphogenetic Proteins), anti-rejection agents, stem cells, and the mixtures thereof.

Preferably, the bone regeneration material according to the invention is intended to be used as an implant or prothesis for a bone formation, a bone regeneration or for a bone correction in a mammal, preferably in a human.

Other embodiments of a bone regeneration material according to the invention are indicated in the appended claims.

The inventions also aims for a medical device containing a bone regeneration material according to the invention.

Other embodiments of a medical device according to the invention are indicated in the appended claims.

The invention also aims for a bone regeneration composition comprising a bone regeneration material according to the invention.

Other embodiments of a composition according to the invention are indicated in the appended claims.

The present invention is also based on a method for enriching a bone regeneration material according to the invention, said method comprising:

Preferably, according to the method according to the invention, said first soaking takes place in a first solution of Ca(NO)·4HO, of CaCl)·2HO, of Ca(OH), CaSO·2HO, or of CaCO.

Advantageously, according to the method according to the invention, said second soaking takes place in a second solution of NaPO, of NaHPO, of NaHPO·HO, of KPOof KHPO, of KHPO, of KHPO, of (NH)PO, of (NH)HPOor of NHHPO.

Other embodiments of a method according to the invention are indicated in the appended claims.

Other characteristics, details and advantages of the invention will emerge from the description given below, in a non-limiting manner and by making reference to the appended figures.

Comparative tests have been carried out in order to determine the calcium and phosphorus quantities (concentrations) salted-out over time (solubility tests) at the start of different bone regeneration materials, this in an medium reproducing the in vivo implantation conditions.

To do this, the calcium and phosphorus ratios and quantities (concentrations) salted-out have been measured in a medium simulating the in vivo implantation conditions (human blood plasma), i.e. in an HBSS medium (Hank's balanced salt medium) having a pH of 7 and of which the composition is outlined in tablebelow:

The following bone regeneration materials have been tested:

The solid phase of hydroxyapatite of natural bovine origin is obtained according to the method described in document WO2015/049336 and is more specifically composed of hydroxyapatite particles having a size of between 0.25 mm and 1 mm.

The materials comprising a first solid phase of hydroxyapatite of natural origin and a second synthetic solid phase of calcium phosphate have been obtained by successive and alternate soakings for a duration of 5 minutes of the first solid phase of hydroxyapatite of natural origin (hydroxyapatite particles) in separate baths of Ca(NO)·4HO (1M, pH=10) and of NaHPO·HO (0.5M, pH=10). The first bath makes it possible to enrich the hydroxyapatite calcium (Ca) particles of natural origin, the second phosphorus (PO) bath.